Given: Radius of the base the cylindrical container =18cm Radius of metal balls =0.9cm Water level raised by 3cm Concept used: Volume of cylinder =πr2h Volume of sphere =(4πr3)∕3 Calculation: Volume of the increased water level =π×182×3 Let n number of metal balls be required According to the question, [(4×π×0.93)∕3}×n=π×182×3 ⇒n=(324×3×3×103)∕(4×93)[∵0.9=9∕10] ⇒n=(324×103)∕(4×81) ⇒n=(324×103)∕324 ⇒n=103 or 1000 ∴ Required number of balls required to raise the water level are 1000